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The rate of ice loss slowed in the first half of July, primarily because of a change in atmospheric circulation. The dipole anomaly, an atmospheric pattern that dominated the Arctic in June, broke down. It was replaced by a pattern of low-pressure systems tracking across northern Eurasia and then into the central Arctic Ocean.

Figure 1. Daily Arctic sea ice extent on July 15 was 8.37 million square kilometers (3.23 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

From July 1 to 15, Arctic sea ice extent declined an average of 60,500 square kilometers (23,400 square miles) per day, 22,500 square kilometers (8,690 square miles) per day slower than the 1979 to 2000 average and substantially slower than the rate of decline in May and June.

Ice extent remained lower than normal in all regions of the Arctic, with open water developing along the coasts of northwest Canada, Alaska and Siberia.

Figure 2. The graph above shows daily Arctic sea ice extent as of July 15, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

As of July 15, total extent was 8.37 million square kilometers (3.23 million square miles), which is 1.62 million square kilometers (625,000 square miles) below the 1979 to 2000 average for the same date, but 360,000 square kilometers (139,000 square miles) above July 15, 2007, the lowest extent for that date in the satellite record.

Through much of May and June, high pressure dominated the Beaufort Sea with low pressure over Siberia. Winds associated with this pattern, known as the dipole anomaly, helped speed up ice loss by pushing ice away from the coast and promoting melt.

However, the dipole anomaly pattern broke down in early July. In the first half of July, cyclones (low pressure systems) generated over northern Eurasia tracked eastward along the Siberian coast and then into the central Arctic Ocean, where they tend to stall. This cyclone pattern is quite common in summer. The low-pressure cells have brought cooler and cloudier conditions over the Arctic Ocean. They have also promoted a cyclonic (anticlockwise) sea ice motion, which acts to spread the existing ice over a larger area. All of these factors likely contributed to the slower rate of ice loss over the past few weeks.

In the last few days, high pressure has started to build again in the Beaufort Sea, but whether this will continue remains to be seen.

Figure 4. In mid-summer, the NASA Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) (left) may show areas of low ice concentration which are actually melt ponds or weather effects. Visible band images from the NASA Moderate Resolution Imaging Spectroradiometer (right) confirm areas of low-concentration sea ice in the interior pack ice. Both images are from July 12, 2010.—Credit: National Snow and Ice Data CenterHigh-resolution image

Areas of diffuse ice

Satellite images provided by the University of Bremen, from the NASA Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E), show areas of low ice concentration over the central Arctic pack ice. While we normally report on the extent of area covered by at least fifteen percent sea ice, a more reliable measurement, it is also valuable to look at ice concentration values, which can reveal conditions in more detail. However, it can be difficult to interpret AMSR-E concentration data during the summer, because microwave signals associated with low ice concentration look very much like signals associated with surface melt. Weather effects can also cause false concentration signals.

By comparing AMSR-E data with data from other satellites, we can determine which areas of apparent low-concentration ice are real, and which appear to be low because of melt or atmospheric effects. Visible-band images from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor show that some of the areas of apparent low ice concentration within the central pack ice are actually melt and atmospheric effects. However, the MODIS data also confirm that there are substantial areas of open water within the pack ice, such as near the North Pole and in the Beaufort Sea.

Open water in the interior pack ice is not unprecedented. Winds can push the ice apart, creating openings in the pack ice. These areas of open water may close up quickly if the wind changes, but since the dark areas of open water readily absorb solar energy, they can also lead to more extensive melt.

Average June ice extent was the lowest in the satellite data record, from 1979 to 2010. Arctic air temperatures were higher than normal, and Arctic sea ice continued to decline at a fast pace. June saw the return of the Arctic dipole anomaly, an atmospheric pressure pattern that contributed to the record sea ice loss in 2007.

Figure 1. Arctic sea ice extent for June 2010 was 10.87 million square kilometers (4.20 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged 10.87 million square kilometers (4.20 million square miles) for the month of June, 1.29 million square kilometers (498,000 square miles) below the 1979 to 2000 average and 190,000 square kilometers (73,000 square miles) below the previous record low for the month of 11.06 million square kilometers (4.27 million square miles), set in 2006. In June, ice extent declined by 88,000 square kilometers (34,000 square miles) per day, more than 50% greater than the average rate of 53,000 square kilometers (20,000 square miles) per day. This rate of decline is the fastest measured for June.

During June, ice extent was below average everywhere except in the East Greenland Sea, where it was near average.

Figure 2. The graph above shows daily Arctic sea ice extent as of July 5, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

At the end of May 2010, daily ice extent fell below the previous record low for May, recorded in 2006, and during June continued to track at record low levels. By the 30th of June, the extent was 510,000 square kilometers (197,000 square miles) below the same day in 2006.

Weather conditions, atmospheric patterns, and cloud cover over the next month will play a major role in determining whether the 2010 sea ice decline tracks at a level similar to 2007, or more like 2006. Although ice extent was greater in June 2007 than June 2006, in July 2007 the ice loss rate accelerated. That fast decline led up to the record low ice extent of September 2007.

However, it would not be surprising to see the rate of ice loss slow in coming weeks as the melt process starts to encounter thicker, second and third year ice in the central Arctic Ocean. Loss of ice has already slowed in the Beaufort and Chukchi Seas due to the tongue of thicker, older ice in the region noted in our April update.

Figure 3. Monthly June ice extent for 1979 to 2010 shows a decline of 3.5% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

June 2010 compared to past years

Average ice extent for June 2010 was190,000 square kilometers (73,000 square miles) less than the previous record low for June, observed in 2006; 620,000 square kilometers (240,000 square miles) below that observed in 2007; and 1.29 million square kilometers (498,000 square miles) below the average extent for the month.

The linear rate of monthly decline for June over the 1979 to 2010 period is now 3.5% per decade. This year’s daily June rate of decline was the fastest in the satellite record; the previous record for the fastest rate of June decline was set in 1999. This rapid decline was in part driven by ice loss in Hudson Bay.

Figure 4. This map of sea level pressure for June 2010 shows a return of the Arctic dipole anomaly pattern, with unusually high pressure (yellow and orange) over the northern Beaufort Sea and unusually low pressure (purple and blue) over the Eurasian coast.—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

The Arctic dipole anomaly

The record low ice extent of September 2007 was influenced by a persistent atmospheric pressure pattern called the summer Arctic dipole anomaly (DA). The DA features unusually high pressure centered over the northern Beaufort Sea and unusually low pressure centered over the Kara Sea, along the Eurasian coast. In accord with Buys Ballot’s Law, this pattern causes winds to blow from the south along the Siberian coast, helping to push ice away from the coast and favoring strong melt. The DA pattern also promotes northerly winds in the Fram Strait region, helping to flush ice out of the Arctic Ocean into the North Atlantic. The DA pattern may also favor the import of warm ocean waters from the North Pacific that hastens ice melt.

June 2010 saw the return of the DA, but with the pressure centers shifted slightly compared to summer 2007. As a result, winds along the Siberian coastal sector are blowing more from the east rather than from the south. Whether or not the DA pattern persists through the rest of summer will bear strongly on whether a new record low in ice extent is set in September 2010.

Figure 5. This satellite image, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA Terra satellite on June 30, 2010, shows that Nares Strait was open and sea ice was flowing through it. Normally Nares Strait remains plugged by an “ice arch” through early July, but this year it was clear by May.—Credit: National Snow and Ice Data Center courtesy NASA/GSFC MODIS Rapid ResponseHigh-resolution image

Nares Strait

Ron Kwok of the Jet Propulsion Laboratory (JPL) reports that Nares Strait, the narrow passageway between northwest Greenland and Ellesmere Island is clear of the ice “arch” that usually plugs southward transport of the old, thick ice in the Lincoln Sea. Typically the ice arch forms in winter and breaks up in early July. This year the arch formed around March 15th and lasted only 56 days, breaking up in May. In 2007 the ice arch did not form at all, allowing twice as much export through Nares Strait than the annual mean. Although the export of sea ice out of the Arctic Ocean through Nares Strait is very small in comparison to the export through Fram Strait, the Lincoln Sea contains some of the Arctic’s thickest ice. For the ice flux rates out of Nares strait, see Figure 5a.

Figure 6. The graph above shows daily Antarctic sea ice extent as of July 5, 2010. The solid light blue line indicates 2010; dashed green shows 2007, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Meanwhile, in Antarctica

At the end of June, Southern Hemisphere mid-winter, the sea ice surrounding Antarctica was more than two standard deviations greater than normal. On June 30, Antarctic sea ice extent was15.88 million square kilometers (6.13 million square miles), compared to the 1979 to 2000 average of 14.64 million square kilometers (5.65 million square miles) for that day.

While recent studies have shown that wintertime Antarctic sea ice has a weak upward trend, and substantial variability both within a year and from year to year, the differences between Arctic and Antarctic sea ice trends are not unexpected. Climate models consistently project that the Arctic will warm more quickly than the Antarctic, largely due to the strong climate feedbacks in the Arctic. Warming is amplified by the loss of ice cover in the Arctic Ocean in areas that had been ice-covered for decades, and by the warming of Arctic lands as snow cover is lost earlier and returns later than in recent decades.

Moreover, rising levels of greenhouse gases and the loss of stratospheric ozone appear to be affecting wind patterns around Antarctica. Shifts in this circulation are referred to as the Antarctic Oscillation (AAO). As greenhouse gases have increased, and especially when ozone is lost in spring, there is a tendency for these winds to strengthen (a positive AAO index). The net effect is to push sea ice eastward, and northward, increasing the ice extent. As the current sea ice anomaly has developed, the AAO index has been strongly positive. See the NOAA AAO Index Web site. For more information about the differences between sea ice dynamics in the Arctic and Antarctic, see the NSIDC All About Sea Ice Web site.

In May, Arctic air temperatures remained above average, and sea ice extent declined at a rapid pace. At the end of the month, extent fell near the level recorded in 2006, the lowest in the satellite record for the end of May. Analysis from scientists at the University of Washington suggests that ice volume has continued to decline compared to recent years. However, it is too soon to say whether Arctic ice extent will reach another record low this summer—that will depend on the weather and wind conditions over the next few months.

Figure 1. Arctic sea ice extent for May 2010 was 13.10 million square kilometers (5.06 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged 13.10 million square kilometers (5.06 million square miles) for the month of May, 500,000 square kilometers (193,000 square miles) below the 1979 to 2000 average. The rate of ice extent decline for the month was -68,000 kilometers (-26,000 square miles) per day, almost 50% more than the average rate of -46,000 kilometers (18,000 square miles) per day. This rate of loss is the highest for the month of May during the satellite record.

Ice extent remained slightly above average in the Bering Sea, and below average in the Barents Sea north of Scandinavia, and in Baffin Bay.

Figure 2. The graph above shows daily sea ice extent as of June 7, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

As we noted in our May post, several regions of the Arctic experienced a late-season spurt in ice growth. As a result, ice extent reached its seasonal maximum much later than average, and in turn the melt season began almost a month later than average. As ice began to decline in April, the rate was close to the average for that time of year.

In sharp contrast, ice extent declined rapidly during the month of May. Much of the ice loss occurred in the Bering Sea and the Sea of Okhotsk, indicating that the ice in these areas was thin and susceptible to melt. Many polynyas, areas of open water in the ice pack, opened up in the regions north of Alaska, in the Canadian Arctic Islands, and in the Kara and Barents and Laptev seas.

The polynyas are clearly visible in high-resolution passive microwave images from the Advanced Microwave Sounding Radiometer (AMSR-E) aboard NASA’s Aqua satellite. What do current ice conditions mean for the minimum ice extent this fall? It is still too soon to say: although ice extent at present is relatively low, the amount of ice that survives the summer melt season will be largely determined by the wind and weather conditions over the next few months.

Figure 3. Monthly May ice extent for 1979 to 2010 shows a decline of 2.4% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

May 2010 compared to past years

Average ice extent for May 2010 was 480,000 square kilometers (185,000 square miles) greater than the record low for May, observed in 2006, and 500,000 square kilometers (193,000 square miles) below the average extent for the month. The linear rate of decline for May over the 1979 to 2010 period is now -2.41% per decade.

The rate of decline through the month of May was the fastest in the satellite record; the previous year with the fastest daily rate of decline in May was 1980. By the end of the month, extent fell near the level recorded in 2006, the lowest in the satellite record for the end of May. Despite the rapid decline through May, average ice extent for the month was only the ninth lowest in the satellite record.

Figure 4. This map of air temperature anomalies for May 2010, at the 925 millibar level (roughly 1,000 meters or 3,000 feet above the surface), shows warmer-than-usual conditions over much of the Arctic Ocean, especially along coastal Siberia. Areas in orange and red correspond to positive (warm) anomalies. Areas in blue and purple correspond to negative (cool) anomalies. —Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

Persistent warmth in the Arctic

Arctic air temperatures averaged for May were above normal, continuing the temperature trend that has persisted since last winter. Temperatures were 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) above average across much of the Arctic Ocean. A strong anticyclone centered over the Beaufort Sea produced southerly winds along the shores of Siberia (in the Laptev and East Siberian seas), resulting in warmer-than-average temperatures in this area. The Canadian Arctic Islands were an exception to the general trend, with temperatures slightly cooler than average over much of the region.

Figure 5. The chart above, from the University of Washington Pan-Arctic Ice Ocean Modeling and Assimilation System, shows anomalies in ice volume by month. Ice volume is expressed in units of 1000 cubic kilometers (240 cubic miles), and is computed relative to averages for the period 1979 to 2009. —Credit: National Snow and Ice Data Center courtesy University of WashingtonHigh-resolution image

Models indicate low ice volume

Ice extent measurements provide a long-term view of the state of Arctic sea ice, but they only show the ice surface. Total ice volume is critical to the complete picture of sea ice decline. Numerous studies indicate that sea ice thickness and volume have declined along with ice extent; unfortunately, there are no continuous, Arctic-wide measurements of sea ice volume. To fill that gap, scientists at the University of Washington have developed regularly updated estimates of ice volume, using a model called the Pan Arctic Ice Ocean Modeling and Assimilation System (PIOMAS).

PIOMAS uses observations and numerical models to make ongoing estimates of changes in sea ice volume. According to PIOMAS, the average Arctic sea ice volume for May 2010 was 19,000 cubic kilometers (4,600 cubic miles), the lowest May volume over the 1979 to 2010 period. May 2010 volume was 42% below the 1979 maximum, and 32% below the 1979 to 2009 May average. The May 2010 ice volume is also 2.5 standard deviations below the 1979 to 2010 linear trend for May (–3,400 cubic kilometers, or -816 cubic miles, per decade).

PIOMAS blends satellite-observed sea ice concentrations into model calculations to estimate sea ice thickness and volume. Comparison with submarine, mooring, and satellite observations help increase the confidence of the model results. More information on the validation methods and results is available on the PIOMAS ice volume Web site.

Further Reading

The SEARCH Sea Ice Outlook, an international, community-wide discussion of the upcoming September Arctic sea ice minimum, is slated to be published in June 2010.

Gridded ICESat data are now available from the NASA Jet Propulsion Laboratory. This data provide an estimate of sea ice thickness based on elevation measurements, from 2004 to 2008.

In May, Arctic air temperatures remained above average, and sea ice extent declined at a rapid pace. At the end of the month, extent fell near the level recorded in 2006, the lowest in the satellite record for the end of May. Analysis from scientists at the University of Washington suggests that ice volume has continued to decline compared to recent years. However, it is too soon to say whether Arctic ice extent will reach another record low this summer—that will depend on the weather and wind conditions over the next few months.

Figure 1. Arctic sea ice extent for May 2010 was 13.10 million square kilometers (5.06 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged 13.10 million square kilometers (5.06 million square miles) for the month of May, 500,000 square kilometers (193,000 square miles) below the 1979 to 2000 average. The rate of ice extent decline for the month was -68,000 kilometers (-26,000 square miles) per day, almost 50% more than the average rate of -46,000 kilometers (18,000 square miles) per day. This rate of loss is the highest for the month of May during the satellite record.

Ice extent remained slightly above average in the Bering Sea, and below average in the Barents Sea north of Scandinavia, and in Baffin Bay.

Figure 2. The graph above shows daily sea ice extent as of June 7, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

As we noted in our May post, several regions of the Arctic experienced a late-season spurt in ice growth. As a result, ice extent reached its seasonal maximum much later than average, and in turn the melt season began almost a month later than average. As ice began to decline in April, the rate was close to the average for that time of year.

In sharp contrast, ice extent declined rapidly during the month of May. Much of the ice loss occurred in the Bering Sea and the Sea of Okhotsk, indicating that the ice in these areas was thin and susceptible to melt. Many polynyas, areas of open water in the ice pack, opened up in the regions north of Alaska, in the Canadian Arctic Islands, and in the Kara and Barents and Laptev seas.

The polynyas are clearly visible in high-resolution passive microwave images from the Advanced Microwave Sounding Radiometer (AMSR-E) aboard NASA’s Aqua satellite. What do current ice conditions mean for the minimum ice extent this fall? It is still too soon to say: although ice extent at present is relatively low, the amount of ice that survives the summer melt season will be largely determined by the wind and weather conditions over the next few months.

Figure 3. Monthly May ice extent for 1979 to 2010 shows a decline of 2.4% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

May 2010 compared to past years

Average ice extent for May 2010 was 480,000 square kilometers (185,000 square miles) greater than the record low for May, observed in 2006, and 500,000 square kilometers (193,000 square miles) below the average extent for the month. The linear rate of decline for May over the 1979 to 2010 period is now -2.41% per decade.

The rate of decline through the month of May was the fastest in the satellite record; the previous year with the fastest daily rate of decline in May was 1980. By the end of the month, extent fell near the level recorded in 2006, the lowest in the satellite record for the end of May. Despite the rapid decline through May, average ice extent for the month was only the ninth lowest in the satellite record.

Figure 4. This map of air temperature anomalies for May 2010, at the 925 millibar level (roughly 1,000 meters or 3,000 feet above the surface), shows warmer-than-usual conditions over much of the Arctic Ocean, especially along coastal Siberia. Areas in orange and red correspond to positive (warm) anomalies. Areas in blue and purple correspond to negative (cool) anomalies. —Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

Persistent warmth in the Arctic

Arctic air temperatures averaged for May were above normal, continuing the temperature trend that has persisted since last winter. Temperatures were 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) above average across much of the Arctic Ocean. A strong anticyclone centered over the Beaufort Sea produced southerly winds along the shores of Siberia (in the Laptev and East Siberian seas), resulting in warmer-than-average temperatures in this area. The Canadian Arctic Islands were an exception to the general trend, with temperatures slightly cooler than average over much of the region.

Figure 5. The chart above, from the University of Washington Pan-Arctic Ice Ocean Modeling and Assimilation System, shows anomalies in ice volume by month. Ice volume is expressed in units of 1000 cubic kilometers (240 cubic miles), and is computed relative to averages for the period 1979 to 2009. —Credit: National Snow and Ice Data Center courtesy University of WashingtonHigh-resolution image

Models indicate low ice volume

Ice extent measurements provide a long-term view of the state of Arctic sea ice, but they only show the ice surface. Total ice volume is critical to the complete picture of sea ice decline. Numerous studies indicate that sea ice thickness and volume have declined along with ice extent; unfortunately, there are no continuous, Arctic-wide measurements of sea ice volume. To fill that gap, scientists at the University of Washington have developed regularly updated estimates of ice volume, using a model called the Pan Arctic Ice Ocean Modeling and Assimilation System (PIOMAS).

PIOMAS uses observations and numerical models to make ongoing estimates of changes in sea ice volume. According to PIOMAS, the average Arctic sea ice volume for May 2010 was 19,000 cubic kilometers (4,600 cubic miles), the lowest May volume over the 1979 to 2010 period. May 2010 volume was 42% below the 1979 maximum, and 32% below the 1979 to 2009 May average. The May 2010 ice volume is also 2.5 standard deviations below the 1979 to 2010 linear trend for May (–3,400 cubic kilometers, or -816 cubic miles, per decade).

PIOMAS blends satellite-observed sea ice concentrations into model calculations to estimate sea ice thickness and volume. Comparison with submarine, mooring, and satellite observations help increase the confidence of the model results. More information on the validation methods and results is available on the PIOMAS ice volume Web site.

Further Reading

The SEARCH Sea Ice Outlook, an international, community-wide discussion of the upcoming September Arctic sea ice minimum, is slated to be published in June 2010.

Gridded ICESat data are now available from the NASA Jet Propulsion Laboratory. This data provide an estimate of sea ice thickness based on elevation measurements, from 2004 to 2008.

During April, Arctic sea ice extent declined at a steady pace, remaining just below the 1979 to 2000 average. Ice extent for April 2010 was the largest for that month in the past decade. At the same time, changing wind patterns have caused older, thicker ice to move south along Greenland’s east coast, where it will likely melt during the summer. Temperatures in the Arctic remained above average.

Figure 1. Arctic sea ice extent for April 2010 was 14.69 million square kilometers (5.67 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged 14.69 million square kilometers (5.67 square miles) for the month of April, just 310,000 square kilometers (120,000 square miles) below the 1979 to 2000 average. The rate of ice extent decline for the month was also close to average, at 41,000 kilometers (16,000 square miles) per day. As a result, April 2010 fell well within one standard deviation of the mean for the month, and posted the highest April extent since 2001.

Ice extent remained slightly above average in the Bering Sea and Sea of Okhotsk, and slightly below average in the Barents Sea north of Scandinavia, and in Baffin Bay, where ice extent remained below average all winter.

Figure 2. The graph above shows daily sea ice extent as of May 3, 2010. The solid light blue line indicates 2010; dashed green shows 2007; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

The very late maximum ice extent, on March 31, means that the melt season started almost a month later later than normal.

As we noted in last month’s post, the late growth in ice extent came largely from expansion in the southernmost Bering Sea, Barents Sea, and Sea of Okhotsk. These areas remained cool, with northeasterly and northwesterly winds, keeping the overall ice extent close to the average for the month of April.

Figure 3. Monthly April ice extent for 1979 to 2010 shows a decline of 2.6% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

April 2010 compared to past years

Average ice extent for April 2010 was 820,000 square kilometers (317,000 square miles) greater than the record low for April, observed in 2007, and 310,000 square kilometers (120,000 square miles) below the average extent for the month. The linear rate of decline for April over the 1979 to 2010 period is now 2.6% per decade.

Figure 4. This map of air temperature anomalies for April 2010, at the 925 millibar level (roughly 1,000 meters or 3,000 feet above the surface), shows warmer-than-usual conditions over much of the Arctic Ocean and northern Canada. Areas in orange and red correspond to positive (warm) anomalies. Areas in blue and purple correspond to negative (cool) anomalies. —Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

Continued high temperatures in the Arctic

Despite the late ice growth, Arctic air temperatures remained persistently warmer than average throughout the winter and early spring season. April temperatures were about 3 to 4 degrees Celsius (5 to 7 degrees Fahrenheit) above average across much of the Arctic Ocean, and up to 10 degrees Celsius (18 degrees Fahrenheit) above normal in northern Canada. Conditions in the Arctic were part of a trend of warmer temperatures worldwide in the past few months. An exception was the Sea of Okhotsk, where cool April conditions and northerly winds have slowed the rate of ice retreat. Visit the NASA GISS temperatures Web site for more information on global and Arctic temperatures over the past few months.

Figure 5. This map of sea ice concentration for April 19, 2010, based on data from the NASA AMSR-E sensor, shows polynyas (blue) in the Bering Sea, and scattered ice cover in the Barents Sea and Sea of Okhotsk. —Credit: National Snow and Ice Data Center courtesy University of Bremen IUPHigh-resolution image

A closer look

While NSIDC primarily uses the Special Sensor Microwave/Imager (SSM/I) and Special Sensor Microwave Imager/Sounder (SSMIS) sensors to track long-term conditions, we also look at data from higher-resolution sensors to assess current conditions in more detail. An image from NASA’s Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) sensor from April 19 reveals numerous polynyas, or areas of open water in the pack ice in the Bering Sea, and broad areas of more scattered ice cover in the Sea of Okhotsk, Barents Sea, and Hudson Bay. Such conditions usually indicate that ice is about to retreat rapidly. Over much of the coastline in this image, there is an indication of low-concentration sea ice. This is an artifact of mixed pixel areas, which contain both water and land. The same effect is seen occasionally in the SSM/I record.

For more information about the satellites NSIDC uses to track sea ice, see the Arctic Sea Ice News Frequently Asked Questions Web page.

Figure 6. A change in wind patterns from February to March started to increase ice flow out of the Arctic along the coast of Greenland. —Credit: National Snow and Ice Data Center courtesy Chuck Fowler and Julienne StroeveHigh-resolution image

Ice motion in the Arctic Ocean

The thickness of sea ice at the beginning of spring plays a role in how much ice survives summer melt, so we pay attention to factors that influence ice thickness, such as ice motion. Ice motion is determined by winds and other factors, which in turn are influenced by weather patterns such as the Arctic Oscillation.

In February, the strongly negative phase of the Arctic Oscillation was associated with a strong Beaufort Gyre, enhancing ice motion from the western to the eastern Arctic. A weaker Transpolar Drift Stream also slowed the movement of ice from the Siberian coast of Russia across the Arctic basin, and reduced ice flow out of Fram Strait. The wind pattern changed in March, when the Arctic Oscillation went into a more neutral phase. As a result, the flow of ice sped up through Fram Strait and along the coast of Greenland. This pattern helps to remove older ice from the central Arctic, pushing it toward the warm waters of the North Atlantic, where it will melt.

In past decades, a strong Beaufort Gyre tended to retain old, thick ice in the Arctic Ocean. However, this may no longer hold true, because in recent years ice transiting the Beaufort Gyre tends not to survive the summer melt season. This summer’s weather conditions may be key to the survival of this older ice. For more information about the Beaufort Gyre and Transpolar Drift Stream, see the All About Sea Ice: Circulation Web page.

Further Reading

The SEARCH Sea Ice Outlook, an international, community-wide discussion of the upcoming September Arctic sea ice minimum, is once again underway. This year, a companion effort, the Sea Ice for Walrus Outlook (SIWO), will provide assessments and short-term (7- to 10- day) predictions of ice conditions in the Alaska region. SIWO is a resource for Alaska subsistence hunters, coastal communities, and other interested parties. See their Web page for regular updates and high-resolution satellite imagery of the region.

The University of Washington Polar Science Center has begun providing Arctic sea ice volume anomalies. Routine, long-term observation records of ice volume are limited, so the anomalies are calculated by assimilating observations of sea ice concentrations into model simulations. The anomalies are updated every few days.

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.

In February, Arctic sea ice extent continued to track below the average, and near the levels observed for February 2007. Ice extent was unusually low in the Atlantic sector of the Arctic, and above normal in the Bering Sea. Meanwhile, Antarctic sea ice reached its summer minimum, near the average for 1979 to 2000.

Figure 1. Arctic sea ice extent for February 2010 was 14.58 million square kilometers (5.63 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged for February 2010 was 14.58 million square kilometers (5.63 million square miles). This was 1.06 million square kilometers (409,000 square miles) below the 1979 to 2000 average for February, but 220,000 square kilometers (85,000 square miles) above the record low for the month, which occurred in February 2005.

Ice extent was above normal in the Bering Sea, but remained below normal over much of the Atlantic sector of the Arctic, including the Barents Sea, part of the East Greenland Sea, and in the Davis Strait.

Figure 2. The graph above shows daily sea ice extent as of March 2, 2010. The solid light blue line indicates 2009/2010; dashed green indicates 2006/2007; dark blue shows 2004/2005 (the record low for the month of February); and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

During February 2010, ice extent grew at an average of 25,700 square kilometers (9,900 square miles) per day. Sea ice extent increased at a fairly steady rate in the early part of the month and then slowed after the middle of February. Ice extent remained more than two standard deviations below the 1979 to 2000 average throughout the month.

Figure 3. Monthly February ice extent for 1979 to 2010 shows a decline of 2.9% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

February 2010 compared to past years

The average ice extent for February 2010 was the fourth lowest February extent since the beginning of the modern satellite record. It was 220,000 square kilometers (85,000 square miles) higher than the record low for February, observed in 2005. The linear rate of decline for February is now 2.9% per decade.

As noted previously, the Arctic Oscillation has been extremely negative this winter, with unusually high surface pressure over the Arctic Ocean. Following a strong negative phase from mid-December through mid-January, the AO briefly went positive, but then dipped again to a strongly negative phase. For more information on the Arctic Oscillation, see the NOAA Climate Prediction Center Web site.

The strong negative AO has contributed to cold temperatures throughout much of the U.S. and northern Europe, and the notable snow events in the eastern U.S. However, the impact on the Arctic has been quite different. First, a negative AO tends to bring warmer than normal temperatures to the Arctic. This factor contributed to the low ice conditions in the Atlantic side of the Arctic, discussed above. Second, the AO has a strong effect on Arctic sea ice motion. The pattern of winds associated with a strongly negative AO tends to reduce export of ice out of the Arctic through the Fram Strait. This helps keep more of the older, thicker ice within the Arctic. While little old ice remains, sequestering what is left may help keep the September extent from dropping as low as it did in the last few years. Much will depend on the weather patterns that set up this spring and summer.

Figure 5. The blue bars represent the average sea ice area on Canada’s east coast for the first three weeks of February, from 1969 to 2009. The red bar shows the sea ice area for the same period in 2010.—Credit: Data is from Environment Canada’s Canadian Ice ServiceHigh-resolution image

Ice conditions off the Canadian east coast

Tom Agnew, Stephen Howell, and Lionel Hache of Environment Canada note that average ice conditions off the east coast of Canada were at record lows during the first three weeks of February. Sea ice charts prepared by the Canadian Ice Service show that ice coverage in the Labrador Sea and Gulf of St. Lawrence was the lowest for that time period since analysts started charting the region in 1969. Mild temperatures and predominately northeasterly winds have prevented both the advance of ice down the Labrador coast and the formation of ice in the Gulf of St. Lawrence. These ice conditions are also linked to the strong negative Arctic Oscillation pattern.

Figure 6. The graph above shows daily Antarctic sea ice extent as of March 2, 2010. The solid light blue line indicates 2009/2010; dashed dark blue indicates 2008/2009; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

A brief look at Antarctic sea ice

While our analysis focuses on Arctic sea ice, we note that Antarctic sea ice has reached its summer minimum extent for the year, at 2.87 million square kilometers (1.11 million square miles). This was 88,500 square kilometers above the 1979 to 2000 average minimum. Through the austral summer, the total extent of sea ice surrounding the Antarctic continent has remained within two standard deviations of the 1979 to 2000 average.

Sea ice extent in the Antarctic has been unusually high in recent years, both in summer and winter. Overall, the Antarctic is showing small positive trends in total extent. For example, the trend in February extent is now +3.1% per decade. However, the Amundsen and Bellingshausen Seas show a strong negative trend in extent. These overall positive trends may seem counterintuitive in light of what is happening in the Arctic. Our Frequently Asked Questions section briefly explains the general differences between the two polar environments. A recent report (Turner, et. al., 2009) suggests that the ozone hole has resulted in changes in atmospheric circulation leading to cooling and increasing sea ice extents over much of the Antarctic region.

Despite cool temperatures over most of the Arctic Ocean in January, Arctic sea ice extent continued to track below normal. By the end of January, ice extent dropped below the extent observed in January 2007. Ice extent was unusually low in the Atlantic sector of the Arctic, the one major area of the Arctic where temperatures remained warmer than normal.

Figure 1. Arctic sea ice extent for January 2010 was 13.78 million square kilometers (5.32 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged for January 2010 was 13.78 million square kilometers (5.32 million square miles). This was 1.08 million square kilometers (417,000 square miles) below the 1979 to 2000 average for January, but 180,000 square kilometers (69,000 square miles) above the record low for the month, which occurred in January 2006.

Ice extent remained below normal over much of the Atlantic sector of the Arctic, including the Barents Sea, part of the East Greenland Sea, and in Davis Strait. The only region with above-average ice extent was on the Pacific side of the Bering Sea.

Figure 2. The graph above shows daily sea ice extent as of February 1, 2010. The solid light blue line indicates 2009/2010; dashed green indicates 2006/2007; light green shows 2005/2006 (the record low for the month of January); and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

During January 2010, ice extent grew at an average of 34,000 square kilometers (13,000 square miles) per day. Sea ice extent increased at a fairly steady rate in the early part of the month and then slowed towards the end of January. A brief slowdown in ice growth is not unusual during winter.

Looking over the entire season, this winter continues the recent trend of slower Arctic ice growth. During the 1980s, the average rate of ice growth for January was approximately 90,000 square kilometers (35,000 square miles) per day. In comparison, during the 1990s, the average rate of January growth fell to about 40,000 square kilometers (15,000 square miles) per day. Including 2010, the average for the 2000s is 39,000 square kilometers (15,000 square miles) per day.

Figure 3. Monthly January ice extent for 1979 to 2010 shows a decline of 3.2% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

January 2010 compared to past years

While Arctic sea ice extent has declined in all seasons, the downward trends in winter ice extent are much smaller than in summer. Polar darkness and low temperatures mean that the ice generally refreezes to about the same boundaries each winter. Ice extent averaged for January 2010 was the fourth lowest for the month since the beginning of satellite records, and 180,000 square kilometers (69,000 square miles) higher than the record low January extent observed in 2006. The linear rate of decline for January is now 3.2% per decade.

Figure 4. The map of sea level pressure anomalies (in millibars) for January 2010 shows higher than average pressures over western Europe and Asia (areas in orange and red) and lower than average pressures over the central Arctic Ocean (areas in blue and purple. —Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

A shift in atmospheric circulation

As discussed in our January post, December 2009 was characterized by an extreme negative phase of the Arctic Oscillation, with the Arctic Ocean dominated by unusually high surface pressure and air temperatures. In January, the Arctic Oscillation shifted from strongly negative to neutral in the middle of the month, and then back to a negative phase at the end of the month. For more information on the Arctic Oscillation, see the NOAA Climate Prediction Center Web site.

In contrast to December, January saw unusually low pressure over the central Arctic and unusually high pressure over western Europe and Asia. While temperatures over much of the central Arctic Ocean were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below normal, temperatures in the Kara and Barents seas were 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) warmer than normal. Ice extent was far below normal in the Kara and Barents seas, keeping the total Arctic sea ice extent below average.

Figure 5. This map of the Arctic shows how earlier melt onset (left) and later freeze onset (middle) have contributed to a longer melt season (right), over the past 30 years.—Credit: NASA Earth Observatory image by Robert Simmon, based on data from Jeffrey Miller and Thorsten Markus, NASA GSFC.High-resolution image

Slow freeze-up keeps ice extent low

Analysis of data from the last three decades shows that the summer Arctic sea ice melt season now lasts nearly a month longer than it did in the 1980s. A later start of freeze-up and an earlier start to the melt season both contribute to the change. A recent paper by Thorsten Markus at NASA Goddard Space Flight Center suggests that the later freeze-up is the dominant factor lengthening the melt season. The analysis shows that, on average, autumn freeze-up starts nearly four days later each decade. Extensive open water at the end of the summer melt season, combined with warmer autumns, delay the autumn freeze-up. The larger expanses of open water absorb more solar energy, and before ice can form again, that heat must be released back to the atmosphere. This trend is most pronounced in the Beaufort, Chukchi and Laptev seas.

Arctic sea ice extent at end of December 2009 remained below normal, primarily in the Atlantic sector of the Arctic. Average air temperatures over the Arctic Ocean were much higher than normal for the month, reflecting unusual atmospheric conditions. Finally, we provide a review of 2009 Arctic sea ice conditions.

Figure 1. Arctic sea ice extent for December 2009 was 12.48 million square kilometers (4.82 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged over December 2009 was 12.48 million square kilometers (4.82 million square miles). This was 920,000 square kilometers (350,000 square miles) below the 1979 to 2000 average for December, but 210,000 square kilometers (81,000 square miles) above the record low for the month, which occurred in December 2006. Ice extent was less than normal over much of the Atlantic sector of the Arctic, including the Barents Sea, part of the East Greenland Sea, and in Davis Strait.

Figure 2. The graph above shows daily sea ice extent as of January 4, 2010. The solid light blue line indicates 2009/2010; dashed green indicates 2007/2008; dark blue shows 2006/2007 (the record low for the month of December); and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

During December 2009, ice extent grew at an average of 68,000 square kilometers (26,000 square miles) per day. Sea ice extent increased at a fairly steady rate throughout the month, staying slightly above the levels observed in December 2007.

Figure 3. Monthly December ice extent for 1979 to 2009 shows a decline of 3.3% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

December 2009 compared to past years

December 2009 had the fourth-lowest average ice extent for the month since the beginning of satellite records, falling just above the extent for 2007. The linear rate of decline for December is now 3.3% per decade.

Figure 4. Map of air temperature anomalies for December 2009, at the 925 millibar level (roughly 1,000 meters [3,000 feet] above the surface) for the region north of 30 degrees N, shows warmer than usual temperatures over the Arctic Ocean and cooler than normal temperatures over central Eurasia, the United States and southwestern Canada. Areas in orange and red correspond to strong positive (warm) anomalies. Areas in blue and purple correspond to negative (cool) anomalies. —Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

Warm air keeps ice extent low

December air temperatures over the Arctic Ocean region, eastern Siberia, and northwestern North America were warmer than normal. In contrast, temperatures in Eurasia, the United States, and southwestern Canada were below average. The strongest anomalies (more than 7 degrees Celsius/13 degrees Fahrenheit) were over the Atlantic side of the Arctic, including Baffin Bay and Davis Strait, where ice extent was below average.

Figure 5. The map of sea level pressure anomalies (in millibars) for December 2009, shows higher than average pressures over Arctic latitudes (areas in orange and red) and lower than average pressures over north Pacific and North Atlantic oceans (areas in blue and purple.—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

Negative phase of the Arctic Oscillation

These regional contrasts in temperature anomalies resulted from a strongly negative phase of the Arctic Oscillation (AO). The AO is a natural pattern of climate variability. It consists of opposing patterns of atmospheric pressure between the polar regions and middle latitudes. The positive phase of the AO exists when pressures are lower than normal over the Arctic, and higher than normal in middle latitude. In the negative phase, the opposite is true; pressures are higher than normal over the Arctic and lower than normal in middle latitudes. The negative and positive phases of the AO set up opposing temperature patterns. With the AO in its negative phase this season, the Arctic is warmer than average, while parts of the middle latitudes are colder than normal. The phase of the AO also affects patterns of precipitation, especially over Europe.

The phase of the AO is described in terms of an index value. In December 2009 the AO index value was -3.41, the most negative value since at least 1950, according to data from the NOAA Climate Prediction Center.

While a negative AO leads to warmer temperatures over the Arctic, it also tends to reduce the flow of sea ice out of the Arctic by affecting the winds that can export the ice to warmer waters, where it melts. In this way, a negative AO could help retain some the second- and third-year ice through the winter, and potentially rebuild some of the older, multiyear ice that has been lost over the past few years. However, we do not yet know if the strongly negative AO will persist through the winter, or what its net effect will be.

Figure 6. The daily time series for 2009. The gray line shows the 1979 to 2000 climatology, thick blue-gray indicates the 1979 to 2009 climatology, dashed green shows 2007, and 2009 is shown in sky blue. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

2009 year in review

The minimum ice extent in September 2009 was greater than the past two Septembers, but again fell below the long-term average. The melt season began with a young, thin Arctic sea ice cover, suggesting that significant amounts of ice would be lost during the melt season. However, a cooler summer with favorable winds helped preserve the ice.

Despite the cool summer, the ice remained thin and vulnerable at the sea ice minimum, with little of the older, thicker ice that used to characterize much of the Arctic. Recently published research by Barber and colleagues shows that the ice cover was even more fragile at the end of the melt season than satellite data indicated, with regions of the Beaufort and Chukchi Seas covered by small, rotten ice floes.

In the fall, the sea ice froze up in fits and starts. The Northern Sea Route opened in October, even after sea ice extent for the Arctic as a whole had begun to increase. The annual average extent for 2009 was 11.18 million square kilometers (4.32 million square miles), 970,000 square kilometers (375,000 square miles) or 8.0% below 1979 to 2000 average and 740,000 square kilometers (286,000 square miles) or 6.2% below the 1979 to 2008 average.

In November, the average rate of Arctic sea ice growth slightly exceeded the 1979 to 2000 average growth rate for the month. However, at the end of the month, some regions, in particular the Barents Sea and Hudson Bay, still had much less ice cover than normal.

Figure 1. Arctic sea ice extent for November 2009 was 10.26 million square kilometers (3.96 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Arctic sea ice extent averaged over November 2009 was 10.26 million square kilometers (3.96 million square miles). This was 1.05 million square kilometers (405,000 square miles) below the 1979 to 2000 average for November, but 420,000 square kilometers (160,000 square miles) above the record low for the month, which occurred in November 2006. In general, the ice edge is now at or slightly beyond its average location, with two notable exceptions: Hudson Bay and the Barents Sea.

Figure 2. The graph above shows daily sea ice extent as of December 6, 2009. The solid light blue line indicates 2009; dark blue shows 2006, dashed green indicates 2007; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

By November, much of the Arctic is in complete or near complete darkness. Air temperatures fall dramatically and sea ice grows rapidly. During November 2009, extent grew at an average 82,000 square kilometers per day (32,000 square miles per day). The rate of increase in sea ice extent was slower during the first half of November, and faster during the latter half.

Figure 3. Monthly November ice extent for 1979 to 2009 shows a decline of 4.5% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

November 2009 compared to past years

November 2009 had the third-lowest average extent for the month since the beginning of satellite records. The linear rate of decline for the month is now 4.5 percent per decade.

Figure 4. The map of sea level pressure (in millibars) for November 2009, shows low pressure in the North Atlantic and high pressure over Russia, which led to winds that brought warmth to the Barents Sea and pushed the ice northward.—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

Slow ice growth: a tale of two regions

Both Hudson Bay and the Barents Sea have experienced a slow freeze-up this fall. However, the slow sea ice growth in the two regions probably resulted from different processes, highlighting the complex interactions between the sea ice, atmosphere and ocean. In the Barents Sea, ice growth was slowed by winds that pushed the ice northwards into the central Arctic, while warmer-than-usual temperatures contributed to the slow ice growth in Hudson Bay.

The Barents Sea is the deepest of the Arctic coastal seas. It is open on its southern and northern boundaries, allowing winds and currents to move sea ice in and out of the region. In November, southerly winds built up between an area of high pressure over Siberia and low pressure in the northern Atlantic Ocean, in accordance with Buys Ballot’s Law. The winds transported warm air and water from the south, and pushed the ice edge northwards out of the Barents Sea.

In contrast to the Barents Sea, Hudson Bay is a relatively shallow body of water, largely enclosed by land. Ocean waters and sea ice do not flow easily in or out of the bay. The lack of ice in southern Hudson Bay this November is probably related to warmer than normal air temperatures in the region, particularly during the first half of the month.

Air temperatures over Barents Sea were also high during November. While the southerly winds contributed to the warmth, ice-free conditions in the Barents likely also added to the atmospheric heat. Without an insulating cover of sea ice, the ocean releases heat directly to the air.

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.

Sea ice extent grew throughout October, as the temperature dropped and darkness returned to the Arctic. However, a period of relatively slow ice growth early in the month kept the average ice extent low—October 2009 had the second-lowest ice extent for the month over the 1979 to 2009 period.

Figure 1. Arctic sea ice extent for October 2009 was 7.50 million square kilometers (2.90 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data CenterHigh-resolution image

Overview of conditions

Sea ice extent averaged over October 2009 was 7.50 million square kilometers (2.90 million square miles). This was 1.79 million square kilometers (691,000 square miles) below the 1979 to 2000 mean for October, but 730,000 square kilometers (282,000 square miles) above the record low for the month, which occurred in October 2007.

Figure 2. The graph above shows daily sea ice extent as of November 1, 2009. The solid light blue line indicates 2009; dark blue shows 2008, dashed green indicates 2007; light green shows 2005; and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.—Credit: National Snow and Ice Data CenterHigh-resolution image

Conditions in context

In the fall, cold conditions and polar darkness return to the Arctic. As is typical for this time of year, ice growth was brisk in October, growing at an average 96,000 square kilometers per day (37,000 square miles per day).

However, the growth rate slowed for a time in early October, coinciding with strong winds from the south over central Siberia. The winds helped prevent ice from forming along the Siberian coast. At the end of the month, extensive areas of open water regions were still present in the northernmost North Atlantic, and north of Alaska. The ice edge was north of both Svalbard and Franz Josef Land.

Figure 3. Monthly October ice extent for 1979 to 2009 shows a decline of 5.9% per decade. —Credit: National Snow and Ice Data CenterHigh-resolution image

October 2009 compared to past years

The period of slow ice growth at the beginning of the month helped to keep October average ice extent low. Arctic sea ice extent was 950,000 square kilometers (367,000 square miles) below October 2005 and 890,000 square kilometers (340,000 square miles) below that measured in 2008. Although ice extent for October 2009 was 730,000 square kilometers (282,000 square miles) above the record low for the month in 2007, it steepened the linear trend for October slightly to -5.9 % per decade.

Figure 4. The map of sea level pressure (in millibars) from October 1 to 30, 2009 shows a strong high-pressure cell over the Beaufort Sea, and low pressure over the Barents Sea. These pressure patterns led to warm southerly winds.—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences DivisionHigh-resolution image

A warm October

For most of the month, a high-pressure system sat over the Beaufort Sea, while unusually low pressure dominated the Barents Sea. In accord with Buys Ballot’s Law, the area between the two pressure centers saw strong, warm winds blowing from the south. This wind pattern, in conjunction with extensive open water, led to a mean monthly temperature as high as 6 degrees Celsius (11 degrees Fahrenheit) above average in the region between the high and low pressure anomalies (October air temperature map).

Figure 5. This bar graph shows that during years of low sea ice extent, precipitation is typically greater than during high ice extent years. The graph is based on storm counts for September, October, and November, in high and low ice years. High ice years in the study are 1980, 1983, 1986, 1992, 1996; low ice years are 2003, 2005, 2006, 2007, and 2008.)—Credit: National Snow and Ice Data CenterHigh-resolution image

Declining sea ice extent and Arctic storms

A new study by Ian Simmonds and Kevin Keay, at the University of Melbourne in Australia, finds connections between the decline in September sea ice extent and the characteristics of Arctic storms. As ice extent has decreased, Arctic storms have shown a tendency to become more intense, especially in the last few years. The study suggests that low September ice extent, with extensive areas of open water, provides more energy to autumn storms, allowing them to become stronger. The stronger storms also help to break up the ice.

Related research at NSIDC reveals that when September ice extent is unusually low, precipitation linked to Arctic storms tends to be greater than when September ice extent is unusually high (Figure 5). Climate scientists are interested in these studies, because increased autumn snowfall could have effects on both sea ice and permafrost in the Arctic.